That's because the breed-only variants could be gotten by the post pixie the year they were released.
As far as I can tell, these are the variants:


I've got one each of those parentless, but those were the ones I got when they first came out. I'm not sure which variant we're getting via the post pixie; it might be the second of those, or it might be the flop eared bunny, since that was the last release.
We've never actually done a parentless experiment with these, and if we did, we would have to not only exclude bunnies from previous years, but also the ones we get from the post pixie. That would make it very difficult, because almost no one keeps track of that. But if you go through people's gardens, you will find that both of them are very uncommon, particularly parentless.
I think Exterminans might have confirmed that the first bunny is parentless, but we've never actually confirmed the second. Still, if you want to only get eggs from the wild, that's up to you. But don't be too surprised if you DON'T get any of those variants. 
As for new artwork, remember that our new artist only started recently! She probably hasn't had time to think of things like this. 